This invention relates to semiconductor devices. More particularly, it is concerned with semiconductor devices having a body including a matrix of semiconductor material with rods of conductive material embedded therein, and to methods of making ohmic contact to the semiconductor material of the matrix.
Semiconductor devices employing semiconductor-metal eutectic composites which include a matrix of semiconductor material with an array of conductive rods disposed therein have been developed for uses as, for example, power field effect transistors, photodiodes, and photodiode arrays. Examples of such devices are illustrated in U.S. Pat. Nos. 4,724,223 to Ditchek and 4,829,173 to Ditchek et al, which patents are assigned to the assignee of the present invention. These and other semiconductor device structures employing semiconductor-metal eutectic composites require ohmic contacts to the semiconductor material of the matrix. Heretofore ohmic contacts to the surface of a semiconductor-metal eutectic composite body at which the ends of conductive rods were exposed also made ohmic contact to some of the rods in the composite. These rods, in effect, became part of the ohmic contact extending the contact through the wafer.
Under certain circumstances the inclusion of conductive rods as part of the ohmic contact to the semiconductor material has led to some undesired effects. Specifically, the rods in the eutectic composite, although generally parallel, frequently are misaligned to a small extent. This divergence causes variations in spacing between the rods which are part of the ohmic contact and other rods which are part of the gate electrode. The maximum blocking voltage of a transistor is determined by a "punch-through" mechanism, such that breakdown occurs when the depletion zone extends from the gate members to the ohmic contact at the drain. Therefore, if the spacing between the rods of the gate and the rods of the ohmic drain contact are reduced by divergence of the rods, the maximum blocking voltage which can be sustained before "punch-through" occurs is also reduced. As a result, the maximum operating voltage of the device is reduced from that which it would be if the rods were aligned perfectly parallel to each other.